Melting and injection device for plastic materials

ABSTRACT

An arrangement ( 1 ) for melting at least one solid precursor product for polymer production, including:
         a housing ( 2 ) for receiving the solid precursor product by way of an opening,   at least one melting device ( 4 ) arranged in the housing ( 2 ) and so disposed that the solid precursor product can be fed thereto for melting, and at least one —preferably switchable—discharge device ( 5 ) which is connected to an opening of the housing ( 2 ) and which can be connected to an injection unit ( 6 ).

The present invention concerns an arrangement for melting at least one solid precursor product for polymer production having the features of the classifying portion of claim 1 and an apparatus for the production of a polymer molding comprising at least two different solid precursor products.

The invention is concerned with the topic of melting polymers, prepolymers or polymer precursors for subsequently reactive processing.

A wide range of different approaches can be supposed as known as the state of the art for melting solid precursor products in the form of reactive components and subsequent reactive processing. In the case of lactams, in particular ε-caprolactams and subsequent polymerization to give polyamide 6 that is to be viewed primarily in the context of the following processing steps:

The processing of additivated caprolactam-based melts in reactive installations in the context of the resin injection process is known, wherein melting or heating of the precursor products is effected in stirred, generally pressurized or evacuated, vessels. In that case the components are circulated by way of pump or dual-piston systems. A plurality of reactive components are combined in a mixing element from which the reactive mixture is discharged into an open or closed mold. By way of example in that respect attention is directed to DE 1 299 885 and DE 600 31 851 T2.

The discontinuous production of components or blocks on a polyamide basis is further known in the context of production of cast polyamide. In that case the non-additivated monomers are usually melted and stored above melting temperature with the exclusion of moisture in suitably sized containers and are only additivated prior to use.

A further possible way of melting and subsequently processing reactive components, in particular for ε-caprolactam or laurolactam, as described in EP 2 572 851 A1, represents thrust screw plasticization, wherein the melting and injection operations in respect of the respective reactive component are performed in a functional unit.

Particularly for low-viscosity substances it is possible to operate in that context with seals based on polymers (EP 2 454 075 B1). In that respect the heating and melting process is based on both a shearing action and also thermodiffusion.

Comparable thereto piston-based systems are known, primarily for non-reactive systems, in which the substances to be melted are pressed under pressurization conditions by way of the most widely varying kinds of shearing and mixing portions and thus the energy input is maximized in relation to high-viscosity masses. As an example here reference may be directed to DE 10 2006 038 804 B3.

As already stated in DE 1 942 992 piston-based systems are further known, in which the preheated reactive components are already mixed in a single piston and discharged only after initiation of the reaction in order to simplify the sealing effect during the displacement of the injection piston, due to the higher viscosity of the reactive mixture. Particularly for very bulky components like for example rotor blades of wind turbine rotors vacuum infusion with preferably thermosetting resin systems has become established, corresponding approaches based on low-viscosity precursor substances of thermoplastic polymers like ε-caprolactam were described in Composites: Part A 38 (2007) 666-681.

Disadvantages of the State of the Art

In current reactive installations for the processing of reactive components liquefied, low-viscosity, additivated components are continuously heated and circulated under high pressure, this entailing a considerable energy consumption. In addition the components are subjected to a considerable residence time divergence due to the periodic removal of individual aliquots for component production and the feed of new components, which can have a detrimental effect on the stability of the individual components or additives. In particular the additives used for the production of polyamides by anionic polymerization can be damaged or deactivated by premature autopolymerization. In particular a substantially larger melt volume is heated throughout and kept above melting temperature than is necessary at the respective moment in time for processing.

In the case of thrust screw-based systems which can be used for melting and metering corresponding reactive components, there is a negligible residence time divergence unlike the situation when using concepts based on melt storage means. By virtue of the implementation of the melting and injection operation in one functional unit however the required back-flow blocking means is to be viewed as a weak point, which prevents melted material being urged back into the melting region when there is a build-up of pressure and in the injection process. Particularly in the case of low-viscosity systems durable sealing and reproducibility is highly problematic in that case. The energy input due to a shearing action is also negligible, in the case of low-viscosity systems.

The joint injection of the reactive components after previous mixing in an injection piston is to be viewed as a disadvantage in particular in regard to reproducibility and possible deposits in the injection piston used. In addition that principle cannot be economically applied a priori in the case of more complicated and expensive shape geometries and with longer flow paths as the situation would involve hardening prior to complete filling of the component cavity. In addition the injection of a mixture which is already of higher viscosity means that the infiltration of textile reinforcing elements like for example a fiber semi-finished product or preform is made seriously more difficult.

The object of the invention is to provide an arrangement of the general kind set forth and an apparatus for the production of a polymer molding from at least two different solid precursor products, in which the above-discussed problems do not occur or occur at least only to a reduced extent.

That object is attained by an arrangement having the features of claim 1 and an apparatus for the production of a polymer molding from at least two different solid precursor products with at least two such arrangements.

The invention permits a two-stage process in which the melting and injection operation of reactive components can be implemented in different elements of the installation. The melting process is preferably performed in a possibly inertised or evacuated melting arrangement intended for that purpose and which is preferably formed with a housing of a cylindrical configuration. Particularly preferably there is provided at least one feed unit connected to an opening of the housing, for the solid precursor product. The injection process into the cavity of a molding tool of a molding machine is performed by an injection unit separate therefrom.

Unlike the situation in a current reactive installation which operates in a recirculatory mode and in which molten material for a plurality of components is kept at an elevated temperature in the day tank and circulated therein the invention ensures that only those amounts are melted, which are also used for the subsequent processing operation, whereby it is possible to counteract an unnecessary thermal loading on the reactive components over a longer period of time or an uncontrollable residence time divergence.

Advantageous embodiments of the invention are defined in the appendant claims.

In the invention the starting raw substances which are in powder, flake or pellet form (solid precursor products) are passed preferably from above or laterally on to the melting apparatus by means of at least one feed unit. That melting element is preferably of a conical configuration and is operated for example at a temperature which is at least 5° C. above the melting point of the components to be melted.

When the solid precursor product is incident on the surface of the melting apparatus it is melted and collects in molten form in a preferably heated collecting zone disposed therebeneath (for example a melting tank). A fit which is as tight as possible (0.05-2 or 5 mm) between the melting apparatus and the housing ensures that no solids can pass into the collecting zone therebeneath.

When sufficiently melted material is present in the collecting zone the discharge device can be opened whereby the molten material passes to and fills the injection unit.

After filling of the injection unit (in the case of a piston injection unit of the piston antechamber) the discharge device is closed and injection is permitted in the injection direction (for example by piston movement). By virtue of a suitable structural design configuration for the collecting zone it is possible in that way to cover a wide band width in terms of injection volumes. The discharge device preferably has a moveable closure element (slider or flap).

The feed of the solid precursor product by the feed unit can be effected for example by means of a screw, spiral, pump, conveyor belt or vacuum suction conveyor device, optionally supported by discharge aids like vibration discharge means through a shaker channel, an oscillating plate or the like.

The feed unit can be structurally separate from the melting device by a separating device, for example by a cell wheel rotary valve, a flap, diaphragm or sintered disc.

The feed of the solid precursor product can be effected gravimetrically or volumetrically.

There can be provided at least one device for temperature control of the housing, that is separate from the at least one heating device. The temperature control device can be in the form of a heating belt, casing temperature control means, inductive heating, resistive heating or the like.

The melting device is preferably arranged centrally in the housing and is preferably of a cone-shaped or pyramid-shaped configuration, tapering upwardly. Preferably the melting device is arranged displaceably in the housing (for example displaceably in respect of height and/or axially and/or radially).

The melting device can be made for example from metal or ceramic.

Preferably the melting device is structurally so designed that the solid precursor product is passed laterally or from above on to a heated surface inclined relative to the horizontal. Preferably, besides other shapes, a conical shape but also an inclined plate is conceivable (better to clean but less surface area).

Temperature control of the melting device is preferably effected by an internal temperature control means. From the aspect of the temperature range temperature control is to be adapted to the component or components to be melted and will generally be in a range of 70-250° C.

The discharge device can be in the form of an actively actuable discharge valve (or tap, or flap, lock device, pump connection, slider). Actuation of the discharge device can be effected electrically, pneumatically, hydraulically, piezoelectrically or magnetically.

When a pressure regulating device is provided the pressure level can be varied at least in the region of the at least one melting device and/or feed unit by the application of reduced pressure (vacuum) or increased pressure for example of between 0.01 and 10 bars, more especially between 0.2 and 1.5 bars.

There can be provided a device for introducing a protective gas (for example N₂, Ar, synthetic or dried air) into the housing.

There can be provided a filling level sensor (for the solid precursor product and/or the melt). Filling level measurement can be effected both above the melting device and also in the region of the collecting zone or a bypass pipe. Filling level measurement can be effected by capacitive, resistive, conductive, radiometric, inductive, vibronic, gravimetric or sound wave-based measurement principles.

A stirring and/or mixing device for promoting homogenization can be disposed in the collecting zone, possibly integrated into a housing which also optionally rotates.

Measures can be provided for temperature homogenization by means of heat exchangers between the arrangement and the injection unit and/or static mixing portions can be provided.

It is possible to provide an introduction device for introducing fluid or solid additives beneath the melting device.

When melting a plurality of components in corresponding arrangements the volume flows before passing into the cavity of the molding tool can be mixed/homogenized in a separate mixing head/mixing element or in a dedicated cavity which can be attributed to the molding tool.

Preferably additivated mixtures of ε-caprolactam or laurolactam, precursor products of thermoplastic epoxy resins or cross-linking silicones are used as solid precursor products for polymer production.

The solid precursor products may contain additives, in particular for initiation and acceleration of the reaction, regulation of the chain length and the degree of branching, stabilization of the polymers obtained or cross-linked end products (UV protection, flame protection, antioxidants), functional additives, dyes and chromophores, fillers, crystallization aids and nucleation agents, modifiers for improving mechanical properties, in particular impact strength, coupling agents for promoting possible fiber/matrix bonding, removal of troublesome moisture or other low-molecular substances and mold release aids.

It is possible to provide for an introduction of a textile reinforcement or generally separate introduction of fibers and/or fillers into one or more cavities of the molding tool.

The injection of the individual molten precursor products can be effected with a constant volume flow, constant pressure, predetermined pressure or volume profile or intermittently.

Protection is also claimed for a process for melting at least one solid precursor product for polymer production. Therein a first step is placing the solid precursor product in a housing by way of an opening. That is followed by the feed of the solid precursor product, preferably by way of a feed unit (conveyor unit) connected to the housing, to a melting device in the housing. The solid precursor product is melted by the melting device to form a melt. As a result the melt collects in a collecting zone for same. Lastly the melt is also discharged by way of a discharge device connected to the housing to an injection unit connected to the discharge device. In that way the injection unit is filled with the melt. The discharge device is closed prior to injection of the melt into a cavity of a molding tool by way of the injection unit.

Protection is also claimed for a process for the production of a preferably fiber-reinforced plastic component on the basis of the said process for melting at least one solid precursor product for polymer production. In that respect essential steps are mixing of the melts to give a reactive matrix, the preparation of an insert portion or a reinforcing element in a cavity of a molding tool, introduction of the reactive matrix into the cavity of the molding tool, hardening the reactive matrix together with the insert portion or together with the reinforcing element to form a plastic component and removal of the fiber-reinforced plastic component from the molding tool. Optionally the insert portion or the reinforcing element can be in the form of a fiber preform. Optionally it is also possible for the cavity to be evacuated prior to the filling operation. Preferably it is further possible for the melt to be mixed from two different melting devices. In that case mixing can be effected during the injection operation or locally between the cavity and the injection piston. Mixing can also be effected in a mixing element disposed upstream of the cavity (feed head, mixing head, adaptor plate, mixing cavity, static mixer). In particular when an insert portion or reinforcing element is provided in the cavity it is preferably provided that a reactive mixture is introduced into that cavity. The insert portion or the reinforcing element is impregnated or has the mixture injected therearound, in that way. That is followed by hardening of the reactive matrix. Finally the cavity is opened and the component is removed.

Further details of the invention are discussed with reference to FIGS. 1 through 8 for various embodiments by way of example.

FIG. 1 shows a first embodiment having an arrangement 1 which has a housing 2 in which is arranged a preferably heated melting device 4 to which a solid precursor product can be fed by way of a feed unit 3 (here a screw conveyor). The melting device 4 is here conical (cone-shaped) and has an internal temperature control means. In addition there is provided a heating device 13 for heating the walls of the housing 2. The molten material collects beneath the melting device 4 in a collecting zone 8, from where it can be discharged through a switchable discharge device 5. There is provided a filling level sensor 8. Also shown are a device 9 for the introduction of a protective gas and a pressure regulating device 12.

In the variant in FIG. 2 the filling level sensor 7 is in the form of an oscillating fork sensor. The double-headed arrow indicates the adjustability in height of the melting device 4 which here is in the form of an inclined plate. There are provided a stripping device 14 and a slider 10.

FIG. 3 shows an apparatus for the production of a polymer molding from at least two different solid precursor products having at least two arrangements 1 as shown in FIG. 1. The melts are introduced into a cavity of a common molding tool 11 by way of injection units 6. Each discharge device 5 is connected to an injection unit 6 directly or by way of a hose or pipe connection.

FIG. 4 shows the same as in FIG. 3 but with arrangements which substantially correspond to FIG. 2. Here however there is provided a feed unit 3 in the form of a suction conveyor with a storage container 15 and a separating device 16 is shown between the feed unit 3 and the melting device 4, in the form of a cell wheel rotary valve.

FIG. 5 shows modifications in relation to FIG. 4, wherein the discharge devices 5 (switch-over valves) are shown inclined. In addition the conduits between the discharge devices 5 and the melting devices 4 are increased in length. An additional temperature control element 17 is also disposed there, which can also be in the form of a heat exchanger and which can also serve for thermal homogenization of the melt.

In FIGS. 6 through 8 the discharge device 5 (switch-over valve) is not formed by a valve head-valve seat combination but has a closure element 21 in the form of a slider, a seal 18 and the discharge passage 22. The seal 18 can for example comprise a ceramic material. Preferably the seal 18 comprises a plastic, in particular a polymer. In FIG. 6 the front part (shown at the right-hand side) of the seal 18 is fitted on to the piston-shaped closure element 21 of the discharge device 5 and is fixed by a screw 19 and a holding plate 20. In FIG. 7 a single longer seal is disposed around or on the entire front shank region (closure element 21) of the discharge device 5. In contrast FIG. 8 shows a variant in which the preferably polymer seal 18 is applied to the slider (closure element 18) in the form of two mutually spaced, cast sealing rings.

LIST OF REFERENCES

-   1 arrangement -   2 housing -   3 feed unit -   4 melting device -   5 discharge device -   6 injection unit -   7 filling level sensor -   8 collecting zone -   9 device for introducing a protective gas -   10 slider -   11 molding tool -   12 pressure regulating device -   13 heating device -   14 stripping device -   15 storage container -   16 separating device -   17 temperature control element -   18 seal -   19 screw -   20 holding plate -   21 closure element -   22 discharge passage 

1. An arrangement for melting at least one solid precursor product for polymer production, wherein: a housing for receiving the solid precursor product by way of an opening, at least one melting device arranged in the housing and so disposed that the solid precursor product can be fed thereto for melting, and at least one—preferably switchable—discharge device which is connected to an opening of the housing and which can be connected to an injection unit.
 2. An arrangement as set forth in claim 1 wherein there is provided at least one feed unit for the solid precursor product, that is connected to the opening of the housing.
 3. An arrangement as set forth in claim 1 wherein the feed unit is separated from the at least one melting device by a separating device.
 4. An arrangement as set forth in claim 1 wherein there is provided at least one temperature control device, preferably a heating device, for temperature control of the housing of the at least one melting device.
 5. An arrangement as set forth in claim 2 wherein the at least one melting device is of a shape which tapers in the direction of the opening of the feed unit—preferably being of a conical or pyramid shape.
 6. An arrangement as set forth in claim 5 wherein the melting device is so arranged in the housing at the end toward the discharge device that a gap so adapted to the solid precursor product remains between the melting device and the housing that the precursor product is prevented for passing in solid form.
 7. An arrangement as set forth in claim 1 wherein there is provided a pressure regulating device by which an increased pressure or a reduced pressure can be produced at least in the housing and/or in the at least one feed unit.
 8. An arrangement as set forth in claim 1 wherein arranged in the housing is a collecting zone arranged beneath the melting device for receiving molten precursor product, wherein that opening in the housing, to which the discharge device is connected, is arranged in the region of the collecting zone.
 9. An arrangement as set forth in claim 8 wherein there is provided a filling level sensor by which the amount of melted precursor product in the collecting zone can be detected.
 10. An arrangement as set forth in claim 8 wherein a stirring and/or mixing device is arranged in the collecting zone.
 11. An arrangement (1) as set forth in claim 1 wherein the housing is connected to a device for the introduction of a protective gas.
 12. An arrangement as set forth in claim 1 wherein the at least one melting device is arranged displaceably in the housing.
 13. An arrangement as set forth in claim 1 wherein there is provided a slider displaceable along a surface of the at least one melting device.
 14. An arrangement as set forth in claim 1 wherein the at least one discharge device is connected to at least one injection device—preferably a piston injection device.
 15. An arrangement as set forth in claim 14 wherein the injection device is connected to a molding tool.
 16. An arrangement as set forth in claim 14 wherein the volume of the collecting zone is less than the volume of 10 times—preferably less than the volume of 3 times—the amount of the material necessary to fill the injection device.
 17. An arrangement as set forth in claim 1, wherein the discharge device has a discharge passage, a closure element which is moveable, preferably slidable, in the discharge passage and a seal between the closure element and the discharge passage, which seal is preferably made from plastic or ceramic and is preferably arranged at the closure element.
 18. Apparatus for the production of a polymer molding from at least two different solid precursor products, wherein for at least two of the at least two different solid precursor products for the melting operation there is provided a respective arrangement as set forth in claim 1 and the molten precursor products can be fed to a common molding tool.
 19. A process for melting at least one solid precursor product for polymer production, in particular in an arrangement as set forth in claim 1, comprising the following steps: receiving the solid precursor product in a housing by way of an opening, feeding the solid precursor product to a melting device arranged in the housing, preferably by way of a feed unit connected to the housing, melting the solid precursor product by the melting device to give a melt, and discharging the melt by way of a discharge device connected to the housing to an injection unit connected to the discharge device.
 20. A process for the production of a fiber-reinforced plastic component comprising the steps: melting at least two solid precursor products in accordance with a process as set forth in claim 19, mixing the melts to give a reactive matrix, providing an insert portion or a reinforcing element in a cavity of a molding tool, introducing the reactive matrix into the cavity of the molding tool, hardening the reactive matrix together with the insert portion or together with the reinforcing element to give a plastic component, and removing the fiber-reinforced plastic component from the molding tool. 